This invention relates generally to the testing of semiconductor integrated circuits (ICs) and devices, and more particularly the invention relates to long term testing of such circuits and devices in a heated environment.
In the electrical probing and measuring of electrical parameters of integrated circuits and devices in semiconductor wafers, a probe card with multiple pins facilitates concurrent access to a large number of circuit contacts in one or more devices in the wafer. Typically one or more probe cards are horizontally arranged parallel to and spaced from the wafer so that “massively parallel” measurements can be made on a single wafer. Alternately, a single card with multiple pin probes and multiple landing patterns can be made, but the demands on materials, manufacturing, and planarity of the multiple landing sites makes it prohibitively expensive.
The long term testing of semiconductor devices, such as electro-migration, time dependent dielectric breakdown, and negative temperature bias instability, is undertaken to determine long term stability and lifetime of the device. To shorten the time required for such tests, the tests are often performed at elevated temperatures between 125° C.–400° C.
Major problems arise from heating of the probe card and probe head system. The horizontal probe card is the closest component to the hot chuck which holds the semiconductor wafer and can suffer a drastic degradation in performance due to temperature dependent leakage current. The large exposed area of the horizontal probe card exacerbates the degradation in probe performance. Material selection for the probe card can reduce the temperature dependent problems, but costs and special material processing considerations limit the practicality of using such materials as ceramics and liquid crystal polymers, for example, when compared to conventional materials used in printed circuit board manufacturing.
Another problem relates to heating of the cabling system necessary in connecting the multiple pins of the probe cards to test apparatus. To keep the cabling system within a manageable size, a custom flexible (flex) cable is typically employed. However, convective flow of hot air from the hot wafer chuck can cause unacceptable electrical leakage of current through the flex cable. The material used in these lower-cost flexible printed circuits, and in particular the adhesive used therein, has low (e.g. 40° C.–80° C.) glass transition temperature (Tg), and electrical leakage between traces will render the cable useless at temperatures higher than Tg. Other materials, such as liquid crystal polymers and high glass transition, thermally cured adhesives, have better high temperature performance but are much more expensive in a system with multiple probe heads and high density of signal traces.
Moreover, the probe card is typically part of a probe head which can be moved in XYZ alignment by manual control knobs. However, the control knobs associated with the probe head can become very hot to touch.
Therefore, a system with multiple probe heads, each have multiple pin probes, is desirable for long term, highly parallel testing of wafers at elevated temperatures. The present invention is directed to providing such a system which overcomes problems associated with conventional test probe heads and systems.